Salmon and Protected Areas

Adelaide Robinson

Background and Motivation

• Many populations of anadromous salmon are expected to go extinct within the next 100 years

  • Anadromous fish are born in freshwater, migrate to ocean and return to freshwater to reproduce
  • Most steelhead and all coho populations within California Are Federally listed

• Habitat loss and urban land use are linked with their decline and lowered juvenile survival

Question

How do protected areas impact salmon populations within California?

Data

• California Monitoring Plan for Salmon and Steelhead

  • CDFW and NOAA

  • Monitor and Assemble data on anadromous salmon populations across CA

    • Adult population counts

    • Geospatial data containing the extents of monitored watersheds

• California Protected Area Database

  • Polygons of areas protected for open space across CA

Data Wrangling

Analysis

\(population = B_0 + B_1year_i + B_2PercentProtected_i + B_3year_i * percentprotected_i +E_i\)

• OLS Linear Regression

  • Multiple Regression: Population regressed on percent protected and year
  • Interaction: Percent protected and year
    • The slope of the relationship between year and population count can vary based on %protected.

• \(H_0: B_1 = B_2 = B_3 = 0\)

• \(H_A: B_1 ≠B_2 ≠B_3 ≠ 0\)

• Ran analysis for Both coho salmon and steelhead

Results

term	estimate	std.error	statistic	p.value	conf.low	conf.high
(Intercept)	-729.154459	402.4470207	-1.811802	0.0703888	-1519.1223835	60.8134660
percent_protected	14.830868	6.2720549	2.364595	0.0182859	2.5193783	27.1423570
year	35.368786	12.3969912	2.853014	0.0044416	11.0345881	59.7029838
percent_protected:year	-0.464231	0.1962358	-2.365679	0.0182328	-0.8494246	-0.0790375

Interpretation

• Watersheds with higher numbers of percent protected have higher numbers of fish

  • when year is 0 there will be on average 14 more steelhead for each one unit increase in percent protected

• Increase in percent protected decreases the rate of change in populations over time

  • -0.5 is the difference in the effect of year on steelhead count for every one increase in protected area

• Steelhead are increasing over time

  • when percent protected is 0 on average there will be an increase of 35 fish per year

• Coefficients are statistically significant using a significance level of 0.05, except the intercept.

Limitations and OLS Violations

• True population likely not linear in parameters

• Is there omitted variable bias?

• Error is not normally distributed or independent

Lessons and Next Steps

• Although my results were significant, I fail to reject the null due to concerns over OLS violations

  • Other methods besides OLS may be better for answering my question

• Explore the relationship between protected areas and survival in a different way

  • Would be better to look at overwinter survival rate